Gz, a guanine nucleotide-binding protein with unique biochemical properties

Cloning of a complementary DNA (cDNA) for Gz alpha, a newly appreciated member of the family of guanine nucleotide-binding regulatory proteins (G proteins), has allowed preparation of specific antisera to identify the protein in tissues and to assay it during purification from bovine brain. Additionally, expression of the cDNA in Escherichia coli has resulted in the production and purification of the recombinant protein. Purification of Gz from bovine brain is tedious, and only small quantities of protein have been obtained. The protein copurifies with the beta gamma subunit complex common to other G proteins; another 26- kDa GTP-binding protein is also present in these preparations. The purified protein could not serve as a substrate for NAD-dependent ADP- ribosylation catalyzed by either pertussis toxin or cholera toxin. Purification of recombinant Gz alpha (rGz alpha) from E. coli is simple, and quantities of homogeneous protein sufficient for biochemical analysis are obtained. Purified rGz alpha has several properties that distinguish it from other G protein alpha subunit polypeptides. These include a very slow rate of guanine nucleotide exchange (k = 0.02 min^-1), which is reduced greater than 20-fold in the presence of mM concentrations of Mg2+. In addition, the rate of the intrinsic GTPase activity of Gz alpha is extremely slow. The hydrolysis rate (kcat) for rGz alpha at 30 degrees C is 0.05 min^-1, or 200-fold slower than that determined for other G protein alpha subunits. rGz alpha can interact with bovine brain beta gamma but does not serve as a substrate for ADP-ribosylation catalyzed by either pertussis toxin or cholera toxin. These studies suggest that Gz may play a role in signal transduction pathways that are mechanistically distinct from those controlled by the other members of the G protein family

Deriving the Hirshfeld partitioning using distance metrics

A

Monte Carlo Study of the Axial Next-Nearest-Neighbor Ising Model

The equilibrium phase behavior of microphase-forming substances and models is notoriously difficult to obtain because of the extended metastability of the modulated phases. We develop a simulation method based on thermodynamic integration that avoids this problem and with which we obtain the phase diagram of the canonical three-dimensional axial next-nearest-neighbor Ising model. The equilibrium devil's staircase, magnetization, and susceptibility are obtained. The critical exponents confirm the XY nature of the disorder-modulated phase transition beyond the Lifshitz point. The results identify the limitations of various approximation schemes used to analyze this basic microphase-forming model.Comment: 4 pages, 3 figure

Cryogenic mechanisms for scanning and interchange of the Fabry-Perot interferometers in the ISO long wavelength spectrometer

The Infrared Space Observatory (ISO) is an ESA cornerstone mission for infrared astronomy. Schedules for launch in 1993, its four scientific instruments will provide unprecedented sensitivity and spectral resolution at wavelengths which are inaccessible using ground-based techniques. One of these, the Long Wavelength Spectrometer (LWS), will operate in the 45 to 180 micron region (Emery et. al., 1985) and features two Fabry-Perot interferometers mounted on an interchange mechanism. The entire payload module of the spacecraft, comprising the 60 cm telescope and the four focal plane instruments, is maintained at 2 to 4 K by an onboard supply of liquid helium. The mechanical design and testing of the cryogenic interferometer and interchange mechanisms are described

Does ultrasonic dispersion and homogenization by ball milling change the chemical structure of organic matter in geochemical samples?—a CPMAS 13C NMR study with lignin

6 pages, 2 figures, 2 tables, 23 references.Ultrasonic dispersion of geochemical samples suspended in water and subsequent homogenization by ball milling is widely used for fractionation of organic matter. The effect of these treatments on organic matter is investigated with lignin as a model compound. Structural alterations detectable by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy were examined. Comparison of the solid-state 13C NMR spectra of untreated lignin and lignin mixed with quartz or soil did not reveal evidence for structural changes in the organic matter composition after ultrasonic dispersion and subsequent ball-milling. The chemical structure of organic matter in geochemical samples is not affected by these treatments as far as such structural alterations can be detected by solid-state 13C NMR spectroscopy.This work was financially supported by the Deutsche Forschungsgemeinschaft (Ko 1035/6-land 2) and the Deutscher Akademischer Austauschdienst (Ref. 315, D/94/16993).Peer reviewe

Atom trapping with a thin magnetic film

We have created a $^{87}$Rb Bose-Einstein condensate in a magnetic trapping potential produced by a hard disk platter written with a periodic pattern. Cold atoms were loaded from an optical dipole trap and then cooled to BEC on the surface with radiofrequency evaporation. Fragmentation of the atomic cloud due to imperfections in the magnetic structure was observed at distances closer than 40 $\mu$m from the surface. Attempts to use the disk as an atom mirror showed dispersive effects after reflection.Comment: 4 pages, 5 figure

Airborne contamination of forest soils by carbonaceous particles from industrial coal processing

In the German Ruhr-area industrial coal processing emitted large amounts of carbonaceous particles for a century until 1970. Our objectives were to detect the presence of airborne carbonaceous particles and assess their impact on the chemical structure of soil organic matter in two forest soils (Podzols) with potential sources of carbonaceous particles approximately 10 to 30 km away. Contamination was not visible macroscopicaily. Organic matter was characterized in bulk soils and in particle-size separates by elemental analysis, magnetic susceptibility measurement, reflected light microscopy, and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. Organic and mineral horizons contained carbonaceous particles including char, coke, and bituminous coal from coal combustion, coking, coal processing, and steel production. In the organic horizons of both soils we observed a material high in magnetic susceptibility (max. 109 × 10−8 m3 kg−1), whereas in the mineral horizons only the Podzol with an intense intermixing moder-type humus had high magnetic susceptibly. This Aeh horizon was extremely rich in organic carbon (139.4 g organic C kg−1), concentrated in the 20 to 2000 µm size separates. In the second Podzol, like in many natural soils, C concentrations were largest in the <20 µm separates. Bloch decay 13C magic angle spinning (MAS) NMR spectroscopy revealed a highly aromatic structure of the carbonaceous particles. Airborne carbonaceous particles formed a macroscopically indistinguishable mixture with natural soil organic matter and could be present in many soils neighboring industrialized areas.Peer reviewe

A Spectroscopic Survey of Subarcsecond Binaries in the Taurus-Auriga Dark Cloud with the Hubble Space Telescope

We report the results of a spectroscopic survey of 20 close T Tauri binaries in the Taurus-Auriga dark cloud where the separations between primaries and their secondaries are less than the typical size of a circumstellar disk around a young star. Analysis of low-resolution and medium-resolution STIS spectra yields the stellar luminosities, reddenings, ages, masses, mass accretion rates, IR excesses, and emission line luminosities for each star in each pair. We examine the ability of IR color excesses, H-alpha equivalent widths, [O I] emission, and veiling to distinguish between weak emission and classical T Tauri stars. Four pairs have one cTTs and one wTTs; the cTTs is the primary in three of these systems. This frequency of mixed pairs among the close T Tauri binaries is similar to the frequency of mixed pairs in wider young binaries. Extinctions within pairs are usually similar; however, the secondary is more heavily reddened than the primary in some systems, where it may be viewed through the primary's disk. Mass accretion rates of primaries and secondaries are strongly correlated, and H-alpha luminosities, IR excesses, and ages also correlate within pairs. Primaries tend to have somewhat larger accretion rates than their secondaries do, and are typically slightly older than their secondaries according to three different sets of modern pre-main-sequence evolutionary tracks. Age differences for XZ Tau and FS Tau, systems embedded in reflection nebulae, are striking; the secondary in each pair is less massive but more luminous than the primary. The stellar masses of the UY Aur and GG Tau binaries measured from their rotating molecular disks are about 30% larger than the masses inferred from the spectra and evolutionary tracks

Wave Function of the Radion in the dS and AdS Brane Worlds

We study the linearized metric perturbation corresponding to the radion for the generalization of the five dimensional two brane setup of Randall and Sundrum to the case when the curvature of each brane is locally constant but non-zero. We find the wave fuction of the radion in a coordinate system where each brane is sitting at a fixed value of the extra coordinate. We find that the radion now has a mass$^2$, which is negative for the case of de Sitter branes but positive for anti de Sitter branes. We also determine the couplings of the radion to matter on the branes, and construct the four dimensional effective theory for the radion valid at low energies. In particular we find that in AdS space the wave function of the radion is always normalizable and hence its effects, though small, remain finite at arbitrarily large brane separations.Comment: Version which appears in Phys. Rev.